This invention relates generally to a color television camera and more particularly to an improvement in a color-resolving striped filter for use in a color television camera. The camera has a two-tube type of a luminance-separation system, having one camera pick-up tube for luminance signals and one camera pickup tube for color signals.
In general, a color television camera of the two-tube type, of the above mentioned luminance-separation system, has a color-resolving striped filter (hereinafter called a striped filter). This filter is in the optical system of the camera tube for color signals. Color signals are derived by a frequency-separation system or a phase-separation system.
In a color television system, as is well known, the chromaticities of the image-receiving three primary colors are so determined that the chromaticity ranges which can be reproduced will be made as wide as possible, with due consideration given to other conditions. Accordingly, the spectral sensitivity or response (image-pickup characteristic) of a color television camera is made to approximate, as closely as possible, the above mentioned image-receiving three primary colors.
In a so-called three-tube color television camera, it is relatively easy to obtain the above mentioned required image-pickup characteristic. However, in a two-tube color television camera with a striped filter, the image-pickup characteristic departs remarkably from the ideal image-pickup characteristic.
That is, a striped filter transmits the light of subtractive primaries (corresponding to the light resulting from the mixing of two primary colors out of three additive primaries). For example, it is not possible, at the present stage of the art of optical filters, to obtain an ideal characteristic curve of wavelength versus relative response, with respect to each of the lights resulting from the additive mixture of two primary colors of the three primaries red (R), green (G), and blue (B), such as, for example, cyan light, magenta light, and yellow light.
As a consequence, the primary colors are extracted from signals such as signals based on the light of all colors or the signals based on the light of the various mixed colors. The signals are extracted in the matrix circuit of a color television camera. An error arises as a result of a difference between the ideal characteristic and the characteristic of the actual filter produced in accordance with the present art. Color turbidity is produced in the image-pickup picture. Furthermore, there are deviations in the characteristics of the manufactured filters of the same type and differences in their transmissible characteristics, which also cause color turbidity in the pickup picture.